The supplying of liquids into the body of medical patients is effected in many instances from a supply vessel from which the liquid runs out by the influence of gravity. If a higher precision in the rate at which liquid is supplied is required, or if the delivery pressure from gravity is not sufficient, positive-displacement pumps are used. The structural parts of such pumps which come in contact with the liquids are, as a rule, made of plastic articles intended for a single use and which are discarded after such use. These plastic articles should be easy and inexpensive to manufacture. In addition, they should ensure the medically necessary precision and safety.
U.S. Pat. No. 2,915,983 discloses a hose pump wherein a drive shaft is mounted in a housing. The drive shaft has at its end an eccentrially arranged shaft piece extending at an angle. On this shaft piece, a swash plate is mounted which is secured against rotation relative to the housing of the hose pump. Between the swash plate and a cover which closes the housing, a hose section laid in rings is arranged. The ends of the hose section are passed through slots in the cover. The hose ends are brought out of the cover and are connected with a liquid source and with a user. When the drive shaft rotates, the swash plate is caused to wobble, pressing a region of the annular hose section against the cover and squeezing it flat. The flattened region moves during the wobble motion, so that the liquid contained in the annular hose section is pushed forward in the hose.
Hose pumps of the prior art have the disadvantage that insertion of the hose is difficult and requires a certain skill. A section of the hose must be laid in the cover or respectively over the swash plate in rings, while the very long ends are brought out of openings in the cover. The diameter of the annular hose section is not fixed, so that the position of the annular hose section in the hose pump is undefined. If the diameter of this annular hose section is made too large or too small, relative movements between the annular hose section on the one hand and the cover or swash plate on the other hand will occur during the revolving squeezing by the swash plate. These relative movements lead to increased friction and to wear and loss of output. In addition with the hose pumps of the prior art, the insertion of the hose requires a certain degree of experience. If the hose is inserted the wrong way, the pump will deliver in the wrong direction.
Also known, is a hose pump (U.S. Pat. No. 3,720,489) where a swash plate forms the cover of the housing. The annular hose section is installed in an annular groove in the housing. The swash plate is pressed in the direction of the annular groove by a spring. In this hose pump also, the hose may be inserted to any direction with the possibility of connecting the long hose ends protruding from the housing in any manner. This hose pump also does not provide for simple changing of the hose and does not ensure that the hose can be inserted only in a defined position in order to avoid unintended reversal of the delivering direction.
For medical uses, where the hose pump is to deliver, for example, blood or a serum, the hose is used as a disposable or throw-away article. Therefore, it must be easy to remove the hose from the pump and to replace it. Since incorrect insertion of the hose may, in such applications, have serious consequences for the patient, it must be assured that operation of the hose pump is possible only with the hose inserted correctly.